The present invention relates to films and layers of relatively high rigidity and strength, improved transparency and high gloss. The present invention furthermore relates to an economical and environmentally friendly process for the production of films and layers.
EP-A 484 816 and EP-A 484 817 disclose heat-sealable packaging films. The films described consist of a polypropylene base layer and at least one top layer of a propylene polymer, where the base layer is built up from an isotactic polypropylene and the top layer is built up from a copolymer of an xcex1-olefin having 2 to 8 carbon atoms and syndiotactic propylene.
EP-A 589 213 discloses a heat-sealable multilayer polypropylene film, a process for the production thereof, and the use thereof. The multilayer film includes at least one base layer predominantly comprising polypropylene, and at least one top layer. The top layer is sealable and comprises an isotactic homopolymer of an olefin.
Joachim Nentwig, Kunststoff-Folien: Herstellung, Eigenschaften Anwendungen, Carl Hanser Verlag, Mxc3xcnich, Vienna, 1994, gives a comprehensive review of the prior art in plastic films.
The object of the present invention is to provide films and layers of relatively high rigidity and strength, improved transparency and high gloss and an economical and environmentally friendly process for the production of these films and layers.
The object of the present invention is achieved by single- or multilayer films and one or more layers comprising at least one polyolefin molding composition containing at least one polyolefin. The polyolefin is derived from at least one olefin having at least 2 carbon atoms, of the formula Raxe2x80x94CHxe2x95x90CHxe2x80x94Rb. Ra and Rb are identical or different and are a hydrogen atom or a straight-chain or branched C1-C15-alkyl radical, or Ra and Rb, together with the atoms connecting them, form a ring or ring system. The polyolefin is prepared by polymerization using at least one metallocene catalyst. The requisite property profile for polyolefins and therefore polyolefin molding compositions cannot be obtained using conventional known MgCl2/TiCl4/donor catalysts.
The polyolefin can contain up to 10% by weight, preferably up to 5% by weight, of ethylene or a second olefin as defined above as comonomer.